1. Field of the Invention
This invention relates to torsional vibration dampers for rotatable shafts.
2. DESCRIPTION OF THE PRIOR ART
It is known to provide a tuned torsional vibration damper for attachment to a reciprocating engine crankshaft or any rotating part of a power transmission system subjected to torsional vibration. Prior art torsional dampers have, however, displayed certain deficiencies. For example, non-metallic tuning elements have been known to be limited to a relatively short life due to their intrinsic behavior under high-cycle distortion and high temperatures; both common conditions in viscous dampers. Non-metallic tuning elements have also been known to undergo drastic changes in stiffness characteristics with age, vibration amplitude, and temperature, causing significant deterioration in damper effectiveness.
Tuned dampers which rely on non-fixed leaf or spoke springs, such as disclosed in U.S. Pat. No. 3,577,802 to Rumsey, display wear and abrasion at points of sliding contact, indeterminate and variable interleaf friction, non-linearity of stiffness, and adverse effects on the ease of analytical modelling, when laminated springs are used, and large amounts of space lost which should be available for the interia disc.
Tuned dampers, such as disclosed in U.S. Pat. No. 3,653,278 to Brinkman, utilizing the visco-elastic properties of silicone fluids, are subject to alteration in tuning with the inevitable deterioration of the silicone fluid under the shearing end temperature effects found in torsional dampers. The gradual loss in damping capability of a silicone fluid can normally be tolerated to a limited extent by itself. When the silicone fluid is used for tuning, however, the deterioration of the fluid has the compound effect of loss in damping and tuning characteristics.
A form of torsional damper utilizing resilient tuning means is found is U.S. Pat. No. 2,724,983 to O'Connor. The use of torsional shaft, as disclosed by O'Connor, requires additional bearing support for the damper and an overall damper length which is unacceptable for many applications.